So far, a heat-treating apparatus of the vertical type has been widely used for heat-treating the substrates. FIG. 8 illustrates the structure of a conventional heat-treating apparatus of the vertical type. The heat-treating apparatus of the vertical type has a reaction furnace 40. The reaction furnace 40 has a reaction tube 42, a manifold 44 and a quartz base 68. Wafers (substrates) 54 which are the objects to be treated (members to be treated) are mounted on a support fitting (boat) 30 that holds a plurality of pieces of wafers 54 in parallel. The support fitting 30 is installed on a heat-insulating member 52 which is for lowering the temperature at the furnace port portion of the treating furnace 40, and the heat-insulating member 52 is placed on the quartz base 68 made of, for example, quartz having an O-ring 50.
The reaction furnace 40 is sealed by the reaction tube 42 made of silicon carbide (SiC), quartz manifold 44 and quartz base 68. In a high-temperature environment of not lower than 1200° C., it is not allowed to use quartz that can be favorably machined. Therefore, the reaction tube 42 is made of silicon carbide. Further, the silicon carbide is not suited for being machined into a complex shape such as in the intake and exhaust portions at the lower part of the reaction tube. Besides, the temperature is low at the lower part of the reaction tube. Therefore, the manifold 44 is made of quartz.
A gas necessary for the treatment is introduced into the sealed reaction tube 42 through a nozzle 66, and is exhausted from a gas exhaust port 59 installed in the manifold 44.
A heater 46 is arranged on the outer side of the reaction tube 42. The reaction tube 42 as a whole is heated by the heater 46 to adjust the wafer 54 to a desired temperature. In the sealed reaction furnace 40, the wafers 54 are heated at a predetermined temperature in a gaseous environment introduced through the nozzle 66 to thereby execute a predetermined processing.
Here, the environment (purity of gas) plays an important role in the furnace (reaction tube 42). Usually, the interior of the furnace (interior of the reaction tube 42) is so controlled that the pressure becomes negative relative to the exterior of the furnace (atmosphere). In this case, if the sealing portion (contact portion) between the reaction tube 42 and the manifold 44 is leaking, the atmosphere flows into the interior of the furnace from the exterior of the furnace as shown in FIG. 9. Thus, if the atmosphere or impurity infiltrates into the gaseous environment in the furnace, the processing is not executed as desired, and the treated wafers 54 fail to exhibit expected properties.
Further, if the gas temporarily flows in large amounts into the furnace due to a trouble in the apparatus or if the gas exhaust port 59 closes, the pressure in the furnace (in the reaction tube 42) becomes positive relative to the exterior of the furnace (atmospheric pressure). In this case, if there is a leakage between the reaction tube 42 and the manifold 44, the treating gas leaks from the interior of the furnace to the exterior of the furnace as shown in FIG. 10. The treating gas used for the processing may often be a dangerous gas such as being toxic or explosive and, therefore, shall not leak to the exterior of the furnace (atmosphere). That is, the gas shall not leak from the exterior of the furnace to the interior of the furnace, or from the interior of the furnace to the exterior of the furnace.
Therefore, a method can be contrived to prevent the leakage of gas by using an O-ring at a portion (contact portion) between the reaction rube 42 and the manifold 44 like using the O-ring 50 for sealing a gap between the manifold 44 and the quartz base 68 as described above.